Your clones are remarkable! What a great reveal in your final set of pics.
Almost makes me want to pick up a Hayden Christianson figure.
If your mold material is stretchy enough to allow the ball shape to slip through the head while extracting, Try turning your master part, the other way down, making your mold, so that when you cast, you pour through the top of the head. As long your part sets deep enough in the mold, the resulting extra material on the top of the head can be carved off and sculpted to match the master. Hey, it’s gotta beat cutting out a ball joint cavity. I don’t like having to do that either.